Stator-controlled hydraulic motor



May 13., 1969 J. L. LUMMUS ETA!- STATOR-CONTROLLED HYDRAULIC MOTOR Pnd Dec. 19; 1966 Sheet JAMES L. LUMMUS ARTHUR PARK INVENTORS.

BY I v I A TT ORNE Y.

US. C]. 91-93 10 Claims ABSTRACT OF THE DISCLOSURE A hydraulic motor is suspended within a well bore at the lower end of a fluid conduit through which hydraulic fluid is fed to the motor under pressure. The motor includes a resilient stator having a female helical thread within a housing, and a rotor having male helical thread and arranged to rotate within the stator. Fluid is forced down between the rotor and the stator causing the rotor to rotate. Means are provided to improve the operability of such hydraulic motor, including means for forcing the resilient stator inwardly against the rotor. Additional operational improvement means are described including means for reducing vibrations and relief means for bypassing drilling fluid.

This invention relates to well drilling apparatus and more particularly to drilling apparatus which is an improvement in drilling systems involving fluid motors embodying pumping elements using the Moineau pump, for example, as a hydraulic motor.

BACKGROUND Well drilling apparatus using the principles of the Moineau pump is described in US. Patent 3,112,801, issued Dec. 3, 1963, W. Clark et al. The apparatus described in that patent uses a specially designed Moineau pump running backwards as the power source, i.e., hydraulic fluid under pressure is fed to the pump so that the pump acts as a motor. Such motor includes a stator, preferably of a resilient material such as rubber, and a rotor, preferably of stainless steel, and is arranged to rotate within the stator. Ordinarily, the rotor has a male helical single thread, and the stator has a female double helical thread. When the rotor is in engagement with the stator, there are provided a series of pockets. When the device is used as a pump by rotating the rotor by means of a prime mover, the pockets move in an operational manner longitudinally of the pump. The rotor rotates about its own axis and also orbits in a cylindrical path about the axis of the stator. By forcing fluid through the device by means of an external pump, the apparatus is caused to operate as a motor by converting the fluid pressure into rotary motion.

When the Moineau pump is used as a motor for downholed rilling, it is normally connected to the lower end of a string of tubular members extending to the surface and commonly referred to as a string of drill pipe, through which drilling fluid is circulated as described in Patent 3,112,801 supra. The lower end of the drilling apparatus is ordinarily connected through a connecting rod assembly and bearing and drive-shaft assembly to a rotating bit sub which carries a drilling bit.

GENERAL PROBLEMS When drilling with an apparatus utilizing the Moineau type device, stalling sometimes occurs. As the bit on the device is placed against the formation, slippage of fluid may occur between the rotor and stator without doing work, depending on how much weight (or force) is applied to the bit. Force can be applied through the drill nited States Patent "ice string to marine type thrust bearing to the housing of the motor. As more weight is applied to the bit, more horsepower is required to turn the bit. The additional horsepower is obtained by increasing the pressure of the drilling fluid. If too much weight is applied, the hydraulic motor may stall as fluid passes between the rotor and stator without doing work. Two conditions allow this to occur: (1) the flexibility of the resilient thread of the stator allows the threads to be pushed back away from the rotor by the increased pressure of the drilling fluid and turning of the rotor does not occur; and (2) when the threads and rotor operate for a period of time, they, of course, wear, and this wearing allows condition in (1) to occur more quickly.

BRIEF DESCRIPTION OF INVENTION We have an improvement which will allow hydraulic drills such as described above to operate in a manner to reduce the problems listed above. We control the size and flexibility of the threads in the stator by causing the stator to expand toward the rotor. This is preferably accomplished by providing a passage, preferably in the shape of a corkscrew, which follows the stator threads from top to bottom. Means are provided to apply fluid under pressure to this corkscrew-like passage. This fluid under pressure pushes the thread against the rotor. In an especially preferred embodiment we further provide means to control the pressure of fluids in this passage. Thus, the right amount of pressure is applied to the corkscrew passage and expands the stator readily inward against the rotor. By so expanding the stator, we can adjust for wear of the stator. We can also expand the stator inwardly against the rotor by injecting a fluid into the system which causes the stator to swell. We also teach means to reduce horizontal vibrations and further teach means whereby fluids may be circulated, even if the motor stalls, in a manner such that fluid can bypass the normal path between the rotor and stator.

Various objects and a better understanding of the invention can be had from the following description taken in conjunction with the drawings in which:

FIGURE 1 illustrates improvements used in a hydraulic motor useful in drilling holes in the ground;

FIGURE 2 illustrates a cross-sectional view along the line of 2-2 of FIGURE 1;

FIGURE 3 illustrates an enlarged portion of a fragmentary section of FIGURE 1 showing relief valve in a passage in the upper end of the rotor of said device;

FIGURE 4 illustrates another form of means for expanding the stator inwardly against the rotor.

DESCRIPTIONS OF PREFERRED EMBODIMENTS Referring now to FIGURE 1 of the drawing, there is illustrated a drilling apparatus suspended by a tubular conduit 10 within hole 12. Conduit 10 is commonly called a drill string. Drilling fluid is provided under pressure by drilling fluid pump 11 which is connected through conduit 11A to the upper end of drilling string 10. Means for suspending drill strings in boreholes and supplying drilling fluid thereto are well known; therefore, this is shown schematically. The downhole drilling motor includes a stator 14 molded to the interior of housing 16. The stator is illustrated as containing a spiral cavity or passage of elliptical cross-section throughout its full length and is shaped in a regularly recurring wave form similar, for example, to the steering shaft on some electric motors. Mounted within this passage is a rotor 18 which is supported centrally at both ends. The rotor, too, is shaped in regularly recurring wave form. Typically, the stator 14 can be about 14 feet long and its helical threads can have a pitch of about 4 feet. Rotor 18, typically, can have a pitch about half that of the stator. The

lower end of shaft or rotor 18 is connected through a bearing and drive-shaft assembly 20 and bit sub 22 to bit 24. Various means not shown are provided to connect the rotor through a shaft to a rotating bit sub for rotating the bit and various thrust and radial bearings as necessary to insure smooth shaft rotation and transmit weight on the drill string v through housing 16 to the bit. These connecting and bearing means will not be discussed as they are well known in the art such as described in US. Patent 3,112,801. Further, such means are readily available in commercial devices. For example, one commercially available drilling unit using the Moineau pump for drilling is called a Dyna-Drill and is manufactured by Smith Industries International, Inc., 6108 Paramount Boulevard, Long Beach, Calif.

As mentioned above, when the bit on the drilling apparatus is placed against the formation, slippage can occur, depending upon how much weight is applied. When slippage occurs, there is an accompanying reduction in revolutions per minute. By slippage it is meant the passing of fluid downwardly between the rotor and the stator without that portion of the fluid so passing performing work in rotating the rotor.

When the rotor is pressed against the bottom of the well bore it, of course, requires more horsepower to turn it than when it is off bottom. Then to obtain the required horsepower to turn the rotor at the desired speed, one must transmit drilling fluid through conduit 10 at a higher pressure. When the additional pressure is applied downwardly through conduit 10, the resilient stator is frequently deformed, e.g., pushed away from contact with the rotor, thus causing slippage. As more and more weight is added and the horsepower required to turn the bit hecomes more than the horsepower developed by the hydraulic motor, the drilling apparatus stalls. We reduce the problems of stalling and reduction of revolutions per minute by providing means to control the size and flexibility of the threads in the stator. In a preferred embodiment we modify the drilling apparatus by providing a longitudinal passage 26 in the interior of stator 14 which follows the threads of the stator. Thus, we provide a round passage in the shape of a corkscrew down the drilling apparatus. Ordinarily there are two helical threads in the stator. Then there are ordinarily two longitudinal passages 26, one for each thread of the stator.

We shall now discuss one means for supplying hydraulic fluid under pressure to corkscrew passage 26. As shown in FIGURE 1, a conduit 28 extends from corkcrew passage 26 to the surface where it connects to pressure gauge 30 and through valve 32 to a fluid pressure source such as pump 34. Thus by simply opening control valve 32 and observing the pressure registered on gauge 30, one can readily control the fluid pressure within corkscrew passage 26. Corrections can be made to the reading on meter 30 to compensate for the head of liquid in conduit 28 if it becomes important in determining the pressure in corkscrew passage 26. By supplying fluid under pressure to passage 26 we can force stator 14 in toward rotor 18. This eliminates or greatly reduces the deformation discussed above which caused the unwanted slippage. For example, if horsepower requirements go up so as to require an increase in the pressure of the circulating fluid, we can offset tendency of slippage by increasing the pressure of the fluid within passage 26 so that stator 14 will resist the efforts of the higher pressure drilling fluid to deform it.

It may not always be desirable to have a conduit 28 extend from corkscrew passage 26 to the surface. Means are provided in FIGURE 4 for maintaining pressure within the corkscrew passage 26 without such conduit 28. Oil reservoir 36 and a pump 38 are provided. The pump 38, as shown, includes a cylinder 40, a piston 42 and a piston rod 44. An inlet valve 46 permits oil to flow from oil reservoir 36 through check valve 46 into pump 38 beneath piston 42. An outlet valve 48 is provided in the lower end of pump cylinder 40 and permits fluid to flow only from beneath piston 42 outwardly toward corkscrew passage 26. In this embodiment it will be noted that corkscrew passage 26 is in fluid communication with the outlet of valve 48.

Power for pump 38 is obtained from the rotation of rotor 18. A spring 50 urges piston rod 44 inwardly to maintain contact with rotor 18. Rod 44 follows the contour of rotor 18 as the rotor rotates. Thus rotation of rotor 18 causes reciprocation of piston 42 which pumps hydraulic fluid from reservoir 36 into corkscrew passage 26. This builds up the pressure of the fluid in passage 26 and forces the stator threads against the rotor. This has a stiffening effect on the stator and causes it to resist deformation.

It is usually desired to control the revolutions per minute and reduce the effect of previous wear of the stator when maximum horsepower is required. A sensing device is used in conjunction with the corkscrew passage 26 and pump 38 to aid in automatically obtaining this objective. This sensing device adjusts thread tension, depending upon the power demand. It is to be remembered that when power of the hydraulic motor demands go up, the pressure of the drilling fluid in drill string 10 is increased, either by an operator or by automatic means. A sensing piston 52 is provided in cylinder 54 which is in the device adjacent oil reservoir 36. Piston 52 is biased upwardly by springs 56. The interior of cylinder 54 on the upper side of piston 52 is in pressure communication with the interior of drill string 10. Cylinder portion 57 beneath piston 52 is in pressure communication with the fluid in the annulus between the tool and the borehole wall. This latter pressure communication is accomplished by having a wall port 58 in the wall of cylinder 54 below piston 52. Wall port 58 is provided with an impermeable membrane 60. The lower end of cylinder 54 below piston 52 is provided with a port having a valve 62 to provide fluid communication with passage 26. The pressure within reservoir 36 tends to approximate the pressure of the fluid in cylinder 54 below piston 52.

Valve 62 is a type which permits flow of fluid only in one direction from corkscrew passage 26 to chamber position 57. Spring 56 also holds check valve 62 closed. Check valve 62 is thus pressure sensitive and the pressure at which it opens is dependent upon the compression of spring 56. The compression of spring 56 is dependent upon the position of piston 52. The position of pressure-sensitive piston 52 is determined by the differential pressure between that in the drill conduit 10 and that in the annulus exterior of the tool. In general, it can be said that the greater this differential, the more work that the hydraulic motor is doing. To obtain the increased horsepower it is normally desired to increase the stiffness of stator 14. To increase this stiffness or to increase the force of the stator against rotor 18, it is desired to increase the pressure of the fluid in corkscrew passage 26. This is readily accomplished with the embodiments in FIG- URE 4. As the pressure differential increases from the interior of the conduit to the annulus, piston 52 is pushed downwardly, thus compressing spring 57. As spring 57 is compressed it takes a higher pressure in corkscrew passage 26 to open valve 62. Thus, the pressure builds up in corkscrew passage 26.

On the other hand, when the drill pipe pressure is reduced, spring 57 repositions sensing piston 52. This reduces the pressure in corkscrew passage 26 by reducing the pressure required to open valve 62. As the pressure in the corkscrew passage 26 is reduced the threads of the stator become more pliable, thus reducing the revolutions per minute and also permits more slippage but less wear to occur. This feature is desirable when drilling through shale, for example, which is relatively easy to drill. Therefore, a smaller amount of power is required. When less power is required the pressure in the drill string is reduced by the operator at the surface and the rpm. of the drill is reduced.

If, on the other hand, a hard formation is encountered,

one ordinarily wants to increase the pressure on the threads of the stator so that slippage can be reduced, which normally occurs when the bit slows when the drill pipe pressure increases. By increasing the pressure on the threads, the rpm. of the power output is increased. This can be accomplished in the embodiment shown in FIGURE 4 by increasing the pressure in the drill pipe. As described above, this forces piston 52 downwardly causing relief valve 62 to have a higher opening pressure. This higher opening pressure causes the fluid in corkscrew passage 26 to increase. The pressure on the corkscrew passage is thus controlled by the opening pressure of relief valve 62.

It is thus seen that the improvements described above improve the operation of the Moineau-type power drill by (1) giving higher output power when required, (2) reducing wear when less power is required, thus increasing the life of the hydraulic motor, (3) tending to keep the rpm. constant, and (4) giving bit cleaning when less than full power is required by having less pressure drop through the hydraulic motor.

As the rotor 18 rotates in the conventional Moineau pump, there is normally generated considerable vibrations. We have provided means for reducing, if desired, any such vibration. This includes a connecting rod 64 connected by a swivel joint 66 to the top of rotor 18. The intermediate portion of connecting rod 64 passes through a swivel hearing 68 which is supported from housing 16 by webbing 70. As shown in FIGURE 2, fluid can flo'w donwwardly through webbing 70 exterior of the swivel bearing. The upper end of connecting rod 64 is connected to a counterweight 72. Thus as the upper end of rotor 18 goes in one direction with respect to the center of housing 16, weight 72 moves in the opposite direction due to swivel connection 66 and swivel support bearing 68. The amount of weight 72 should be sufficient to counteract the horizontal force of rotor 18. This can conveniently be determined by multiplying the rotor weight times its displacement each revolution. Ordinarily the weight 72 will be in the range from about -15 pounds.

If for some reason the hydraulic motor system of the embodiment shown in this invention should fail, it is desirable to have flow of circulating fluid so that drilling can be continued by rotating the drill pipe from the surface. In order to provide for this continuation of flow, we provide a dump valve 74 as shown in FIGURE 3. As shown therein, we provide a longitudinal passage 76 within rotor 18. Passage 76 communicates through lateral ports 76 with the fluid from drill string 10. Relief valve 74 is provided with a spring 78 so that it will only open when certain pressure differentials are reached and permits flow only downwardly.

As mentioned above, in ordinary drilling sometimes the stator wears and the tool is not as eflicient as it should be. As also taught above, we have discovered that this efficiency can be greatly improved by forcing the stator inwardly against the rotor. In addition to the systems described above for forcing the stator inwardly, we have found that by injecting certain fluids in the circulating streams that flow through the tool, that the stator can be made to swell. When additives are supplied to the circulating fluid to accomplish this, then the stator is indeed forced inwardly toward the rotor as it cannot expand outwardly due to being confined by housing 16. It is desired that the additive swell the resilient material of which the stator is made without deteriorating the resilient material to where it is no longer useful for the purpose intended. For convenience, such additives will herein be called swelling agents. Suitable swelling agents include EP additives such as chlorinated and/or sulfurized fatty acids, some of which are commercially available as DASCO 950-NI, made by Stewart Oil Company of Chicago, Ill.

Other suitable additives are lead napthenate, sold by Witco Chemical Company of Chicago, and mixtures of lead napthenate and DASCO 950-NI with suitable solublizing surfactant. If water is the circulating fluid, the lead napthenate can be mixed in the following proportions to form an emulsion:

Benzene No-Stik 25 Lead napthenate 25 No-Stik is chiefly Emcol HB, an anionic surfactant more accurately defined in US. Patent 2,976,209. Other suitable agents are Sulchlor-lOS; Base -8; Sulchlor 1717, which are sulfurized and/ or chlorinated lard oil sold by Carlisle Chemical Company, Reading, Ohio. Another agent is Bit Lube 111, a sulfurized fatty acid sold by Baroid National Lead Company, Houston, Tex.

In the above description we have discussed the improvements on the hydraulic motor as a power source. However, it is to be understood that the improvement can be used when the device is used as a pump. For example, if the stator in a Moineau-type pump becomes worn, hydraulic fluid can be provided to passage 26 as described above for forcing the stator against the rotor. This will relieve the effects of the wearing of the stator and improve the operation of the Moineau-type pump.

While only a limited number of embodiments have been shown in considerable detail, it is possible to produce other embodiments without departing from the spirit or scope of the invention.

We claim:

1. A hydraulic apparatus for use with a drill bit in a conduit for supplying fluid thereto, which comprises:

a housing;

a resilient stator with female helical threads within said housing; a rotor with male helical thread inserted within said stator and of a character to rotate a drill bit;

expanding means for extending the resilient stator inwardly against said rotor and in which said expanding means comprises a corkscrew-like passage extending through the interior of said stator and means for supplying hydraulic fluid under pressure to said passage, and in which said means for supplying fluid includes limiting means for controlling the pressure of hydraulic fluid in said passage;

said limiting means including an oil reservoir carried by said housing; a cylinder supported by the body of said apparatus; a sensing piston within said cylinder, one said side of said sensing piston being in pressure communication with the interior of said conduit and the other end in pressure communication with the exterior of said body, biasing means urging the piston toward the end in pressure communication with the conduit; fluid connecting means connecting said corkscrew passage and said oil reservoir; a valve in said fluid connecting means opening at a pressure according to the position of said piston, and pump means for pumping oil from said reservoir to said corkscrew passage.

2. An apparatus as defined in claim 1 in which said rotor has longitudinal passage therethrough and a relief valve means in said passage such that when the pressure in said conduit exceeds a given amount over that within said longitudinal passage, said relief valve opens.

3. A well drilling apparatus for use in drilling a borehole in the earth for use with a drill string for supplying fluid thereto, said drilling apparatus having a housing; a resilient stator with female helical threads and within said housing; and a rotor with male helical thread inserted within said stator; the improvement which comprises:

a corkscrew-like passage extended through the interior of said stator and following the threads thereof; means for supplying fluid to said corkscrew-like passage;

sensing means to sense the differences in pressure between fluid in said drill string and that in said borehole exterior said drill string;

said sentsing means including control means responsive to said sensing means for controlling the pressure of fluid within said corkscrew-like passage.

4. The apparatus of claim 3 including:

a connecting rod;

a swivel joint means connecting said connecting rod to the upper end of said rotor;

a swivel bearing means intermediate the ends of said connecting rod and supporting said connecting rod;

means supporting said swivel bearing means from said housing; and

a counterbalancing weight connected to the upper end of said connecting rod above said swivel bearing means.

5. An apparatus as defined in claim 3 in which said rotor has a longitudinal passage therethrough, and relief valve means in said passage such that when the pressure in said conduit exceeds a given amount, said relief valve opens.

6. An apparatus for use with a conduit for supplying fluid thereto, said apparatus having a housing, a resilient stator with female helical threads and within said housing, and a rotor with male helical thread inserted within said stator, the improvement which comprises:

a. connecting rod;

a swivel joint means connecting said connecting rod to the upper end of said rotor;

a swivel bearing means intermediate the ends of said connecting rod and supporting said connecting rod and including means supporting said swivel bearing means from said housing, and

a counterbalancing weight connected to the upper end of said connecting rod above said swivel bearing means, said counterbalancing weight being at least about equal to the weight of said rotor times its displacement each revolution.

7. A 'well drilling apparatus for use with a drill string for supplying fluid thereto, said drilling apparatus having a housing; a resilient stator with female helical threads and within said housing; and a rotor with male helical thread inserted within said stator; a bit driven by said rotor, the improvement which comprises:

said rotor being characterized by having a longitudinal passage therethrough and opening at each end thereof; and

a relief valve means in said passage such that when the pressure in said conduit exceeds a given amount over that within said longitudinal passage, said relief valve opens so that drilling fluid can be transmitted down said drill string, and the longitudinal passage, to said bit.

8. A hydraulic apparatus comprising:

8 a housing; a resilient stator with female helical threads within said housing;

a rotor with male helical thread inserted within said stator and of a character to rotate a drill bit;

expanding means for extending the resilient stator inwardly against said rotor;

a connecting rod;

a swivel joint means connecting said connecting rod to said rotor;

a swivel bearing means supported by said housing above said rotor, said swivel bearing means being intermediate the ends of said connecting rod which extends therethrough;

a counterbalancing weight connected to the upper end of said connecting rod above said swivel bearing means, said counterbalancing weight being at least about equal to the weight of said rotor times its displacement each revolution.

9. A method for use in operating an apparatus having a resilient stator with female helical threads supported within a housing and a rotor with a male helical thread inserted within said stator, said apparatus being used in fluid communication in a drill string suspended in a well bore, the method which comprises:

directing fluid through said conduit;

expanding said stator by including the step of injecting a swelling agent downwardly through said drill string to cause said swelling agent to contact said stator, expanding it against said rotor.

10. A method as defined in claim 9 in which said swelling agent is selected from the following: chlorinated fatty acid, sulfurized fatty acid.

References Cited UNITED STATES PATENTS 459,332 9/1891 Nash 9156 X 2,329,386 9/1943 Brennan 103117 2,532,145 11/1950 Byram 103-117 2,545,604 3/1951 Byram 103-117 2,695,565 11/1954 Seinfeld 103-117 2,874,643 2/1959 Bourke 1031 17 2,957,427 10/1960 OConnor 103-117 X 3,011,445 12/1961 Bourke 1031 17 X 3,028,812 4/1962 Scotti l03117 3,309,999 3/1967 Patterson 9156 X 3,354,537 11/1967 OConnor 103117 X EVERETTE A. POWELL, IR., Primary Examiner.

US. Cl. X.R. 103117 

